Despite the high prevalence of chronic sleep loss in modern society, no animal models have been developed to systematically examine the effects of chronic partial sleep loss on sleep architecture and indices of health. Furthermore, nothing is known about the effects of age or circadian rhythmicity on sleep during adaptation to or recovery from partial sleep restriction. The proposed studies will develop the rat as an animal model to test hypotheses about the impact of age and circadian rhythms on sleep during and following partial chronic sleep restriction. Most of the studies will involve young, middle age and old F344 and WKY rats in which sleep will be moderately (8 hours) or severely (4 hours) restricted for 1, 5 or 10 days. Sleep will be recorded under baseline conditions as well as during and for five days after the sleep restriction period. The circadian rhythms of body temperature and total locomotor activity will be monitored via biotelemetry. Old animals will be divided into two groups for data analysis: those that have robust and intact circadian rhythms and those where the rhythms are severely fragmented. This division, along with studies on animals with lesions of the SCN, will address questions about the importance of the integrity of the circadian system in the response to repeated sleep restriction. Use of F344 and WKY rats will test the hypothesis that the homeostatic sleep recovery process during and following a period of repeated sleep restriction is dependent on baseline sleep architecture. The endocrine and metabolic consequences of chronic partial sleep restriction will be evaluated by examining stress hormones and glucose metabolism under baseline and responsive conditions. The partial chronic sleep restriction paradigm will also be used on an animal model diabetes, the Zucker Fatty Diabetic rat, to determine whether the onset of diabetes occurs prematurely or is more severe in chronically sleep restricted animals. The completion of the proposed studies is expected to provide new insights on the effects of aging on sleep quantity and quality during and following chronic partial sleep loss, and on the physiological consequences of chronic sleep loss as a function of age. These studies will provide new information on the integration of the circadian and homeostatic processes in the regulation of the sleep wake cycle as a function of age, and will lead to new animal models for preventing or attenuating the effects of sleep loss on human health and disease.